Traffic responsive control system

ABSTRACT

In order to provide efficient and safe traffic control at a signal intersection, a system is shown for operating the signal sequence according to detection of the approach, presence and passage of vehicles relative to the intersection. Each approach lane to the intersection is provided with traffic detector, such as an induction loop detector for sensing the presence of an automobile within a circumscribed area. Utilizing this detection feature to its fullest extent, logic circuitry is described responsive to the information generated by the loop detectors and operating the signals, for providing directional traffic flow primarily in accordance with the instantaneous, clear space available within the intersection and protection against conflicting signal indications. Additionally, the circuitry in its preferred form is modulized to provide a separate control unit for each direction of traffic, which units may be conveniently interconnected for providing a wide variety of intersection control functions.

United States Patent [72] Inventors Howard Carmack 17034 Via Margarita,San Lorenzo, Calif.

94580; Richard Urbaniak, 3265 Primrose Lane, Walnut Creek, Calif. 94598[21] Appl. No. 713,831

[22] Filed Mar. 18, 1968 [45] Patented June 1,1971

[54] TRAFFIC RESPONSIVE CONTROL SYSTEM 12 Claims, 8 Drawing Figs.

52 us. Cl 340/37, 340/ 3 8 [51] Int. Cl G08g1/01, 608g 1/02 [50] FieldotSearch 340/37, 38

[56] References Cited UNITED STATES PATENTS 3,430,221 2/1969 Barringeret al. 340/38X 3,464,059 8/1969 Brockett 340/ 3 7 3,473,147 10/1969 Hill340/37 ACH Primary Examiner-Donald .l. Yusko Auomeywarren, Rubin,Brucker and Chickering ABSTRACT: In order to provide efficient and safetraffic control at a signal intersection, a system is shown foroperating the signal sequence according to detection of the approach,presence and passage of vehicles relative to the intersection. Eachapproach lane to the intersection is provided with trafi'ic detector,such as an induction loop detector for sensing the presence of anautomobile within a circumscribed area. Utilizing this detection featureto its fullest extent, logic circuitry is described responsive to theinformation generated by the loop detectors and operating the signals,for providing directional traffic flow primarily in accordance with theinstantaneous, clear space available within the intersection andprotection against conflicting signal indications. Additionally, thecircuitry in its preferred form is modulized to provide a separatecontrol unit for each direction of traffic, which units may beconveniently interconnected for providing a wide variety of intersectioncontrol functions.

VEHICLE CONYROL UNIT REST 95 FIG. 1

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a ATTORNE? S PATENTEU JUN 119m SHEET 2 OF 6 S R I J O N E TMA N NRB .REAR 1 VCU T N T I A HOWARD RICHARD mohomkma 'P ATENTE UJuu 1 I97! SHEET0F 6 VEHICLE UNIT WITH ADVANCE DETECTION AND ALL RED OVERLAP FIG. 6

2 4 8 3 M W 3 M L E A 6 3 w 9 i 6 u e m R R wR Eh ML mm l l T T e W R wa m 4 M N T L M. v m v W a I 2 l K m w/ m R N 0 E I T CT TP VP Em DW D AREST INVENTORS HOWARD CARMACK RICHARD URBANIAK BYzflm/rzafm,

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Mm j ATTORNE 8 FIG. 8

TRAFFIC RESPONSIVE CONTROL SYSTEM The present invention relates totraffic control systems and more particularly to an improved trafficcontrol system which operates on a principle of space allocation ratherthan conventional time allocation.

To provide a background for appreciating the contribution made by thepresent invention to the art, several widely used traffic controltechniques will be considered. The most common type of controller is thefixed time device, wherein traffic lights are set according to asemipermanent time cycle. That is, the time sequence may be adjustedduring the day at the signal station to compensate for variable trafficconditions. in locations where highly varying traffic conditions exist,this is the most inefficient of all the devices.

Another type of system is the semitraffic actuated controller wherein,approaching cross-street traffic is sensed by a vehicle detector, suchas a pressure detector. In the absence of cross street traffic, the mainstreet is provided with a continuous green light. Upon detection of anapproaching cross-street vehicle by the detector, which commonly isplaced about 80 feet from the intersection, the main street green lightis changed through yellow to red and the cross-street signal receives agreen indication. The green proceed indication is maintained for atleast a preselected initial fixed interval sufficient to allow themaximum possible number of cars waiting between the intersection and thevehicle detector, e.g. 80 feet, to pass through the intersectionregardless of the actual number of cars waiting, and for a longer timeinterval if vehicles continue to approach and pass over the detector inclose order. This second, vehicle responsive time interval willterminate upon occurrence of a sufficient gap in the flow of cars, inthis instance 80 feet, or otherwise upon elapse of a preset maximum timeinterval. After such termination, the main street traffic will obtain agreen signal, for an assured preset duration independent of trafficrequirements.

Additionally, there is in use a system characterized as a volume densitycontroller, modifying the above semitraffic actuated controller, inwhich both the initial time interval and the vehicle responsive intervalare varied by the density of traffic flow. That is, the controllercounts cars approaching the intersection during a stop indication andattempts to provide an average initial green interval of sufficientduration to allow the average number of waiting cars to pass through theintersection. Subsequently arriving vehicles in close order extend thegreen light into the vehicle responsive interval as above, however, inthe volume density system the permissible gaps between cars decreaseswith time according to detected and computed average trafiic density,again independently of the instant traffic needs. For example, at firstsubstantial gaps between cars may occur without inducing a redindication, however, as time elapses the permissible gap distancedecreases rapidly when a large number of cars are waiting in the otherapproaches to the intersection arid more slowly when the heavier trafficis in the moving stream.

It will be apparent that all of the above described traffic actuatedsystems attempt to construct a time model of the average traffic at theintersection and control the signal lights according to the modelconditions. Accordingly, such systems, while offering some improvementover entirely fixed time devices, neglect the instantaneous trafficrequirements and make signal control decisions which are to a largedegree arbitrary and inefficient. Moreover, and with particularreference to the volume density system, complex and expensive circuitryis required to achieve the described control functions, wherein theincurred substantial cost of construction and maintenance prohibitswidespread applications of the system.

Accordingly, it is an object of the present invention to provide atraffic responsive control apparatus which is to a large degree moreefficient, more reliable and safer in regulating the movement of trafficthrough an intersection.

It is a still further object of the present invention to provide aversatile traffic control system for performing allocation of availableintersection space, and which is capable of handling a plurality oftraffic phases, i.e. lanes of traffic flow through an intersectionallowing non conflicting concurrent moves safely and efficiently.

A feature and advantage of the instant invention is that pedestriantraffic control may be achieved in combination with vehicle controlutilizing the same basic circuit for both traffic components.

A further feature and advantage of the instant invention is thatpedestrian travel may occur during a slack in the vehicle traffic so asto avoid pedestrian dominance of the intersection.

A still further feature and advantage of the invention is that thesystem may be arranged for concurrent movement of several nonconflictinglanes of traffic. in this same regard, the system may be convenientlyadapted to provide for movement of one lane of traffic during separatemovements of several other traffic lanes, that is, allowing foroverlapping signal controls. Additionally, the system is particularlyadaptable for providing preempter operations, desirable in emergencytraffic situations such as preempting normal traffic flow to allow firevehicles and the like, clear passage.

The present invention possesses other objects, features and advantages,some of which of the foregoing will be set forth in the followingdescription of the preferred form of the invention which is illustratedin the drawings accompanying and forming part of this specification. Itis to be understood, however, that variations in the drawings anddescription may be,

adopted within the scope of the invention as set forth in the claims.

Referring to the d4awings:

FIG. 1 depicts, in block diagram form, the traffic control systemoperating in conjunction with the basic two-way intersection.

FIG. 2 shows a schematic diagram of the control circuitry indicated inFIG. 1.

FIG. 3 is a schematic diagram of a solid-state signal light switchingcircuit utilized in the invention.

FIGS. 4 and 5 are detailed schematic diagrams of electronic timers usedin the various circuits of the invention.

H6. 6 shows a schematic diagram of a more sophisticated control unitincluding the features of advanced vehicle detection and mandatory timedstop intervals between each conflicting traffic movement.

FIG. 7 is a further schematic diagram illustrating a pedestrian signalcontrol unit ofthe present invention.

FIG. 8 shows a typical intersection situation utilizing the system ofthe present invention.

The control system of the present invention to allocate available spacewithin an intersection to approaching traffic. Pursuant to this end, thecontrol apparatus, for most purposes, is solely responsive to vehicle orpedestrian traffic.

Referring to FIG. 1, the invention here includes at least two detectorsl0 and 12 arranged within a preselected area of the approach lanes to anintersection, in this case intersection 14 of two one-way streetapproaches, A and B. Detectors l0 and 12, in this instance, are of thetype which provide for opening and closing of a switch in response tothe presence of a vehicle within the areas bounded by each of therespective loops.

Connected to each of detectors l0 and 12 are vehicle controlunits A andB, 15 and 16, having letters corresponding to approaches A and B, whichare in turn interconnected with one another to insure mutually exclusiveoperation of green or proceed traffic directory conditions for theintersecting traffic. Signal lights 18 and 19, each having red (stop),yellow (caution), and green (proceed) indicator lights, are connectedrespectively to control units 16 and 15 for supervising vehicle trafficalong the respective directions of B and A approaches.

in practice, when both of area detectors l0 and 12 are free of vehicles,indicating no traffic in either the A or B approaches, both of signallights 18 and 19 are in the red or stop condition. Now, as a car entersthe area of one of the detectors, for example, car 11 shown entering thearea of detector 10, the corresponding vehicle control'unit, in thisinstance, unit 15, receives an impetus from the detector which causesthe associated signal, signal light 19, to switch from the red to thegreen condition. As car 11 passes into the intersection proper thusleaving the boundaries of area detector 10, control unit 15, receivesanother impetus which responsively causes signal light 19 to cyclethrough a yellow indication to a red indication. Should a vehicle enterarea detector 12, approaching the intersection in direction B, duringthe time period in which car 11 is receiving a green signal, vehiclecontrol unit 16, is prevented from switching light 18 to the greencondition until car 11 has left the boundaries of detector 11 andentered the intersection. That is, control unit 16 is disabled duringthe actuation of control unit 15. Of course, as soon as car 11 leavesthe area of detector 10, which eventually changes signal light 19 to ared or stop indication, then unit 16, is again operative such that thedetection of a car by area detector 12, causes signal light 18 to switchfrom its normally red or stop indication to the green or proceedindication.

Additionally, several advantageous and preferred features may be addedto this basic operation as discussed more fully hereinafter. Among suchfeatures are a means for detecting a vehicle approach in advance of areadetectors 11 and 12, wherein additional similar detectors are disposedupstreet from area detectors and 12 to allow early switching of thesignal lights to the proceed condition, during light traffic, so thatapproaching cars need not slow down.

Furthermore, circuitry is shown for providing a pedestrian control unitwhich operates in conjunction with the vehicle control unit such asthose shown in FIG. 1, to permit pedestrian traffic to pass duringperiods of nonconflicting vehicular movement.

Referring now to both FIGS. 1 and 2, wherein FIG. 2 schematicallyillustrates the control circuitry for vehicle control units 15 and 16,and the interconnections therebetween as partially shown in FIG. 1. Eachof the control units 15 and 16 are oflike circuitry such that any numberof such units may be cascaded for controlling a corresponding numberoftraffic approaches or phases. This is to be considered an importantadvantage of the invention due to the present day usage of multipletraffic lanes at busy intersections, e.g. rightand left-hand turn lanes.Only the circuitry of vehicle control unit 16, will be described indetail due to such universalness between the units and reference will bemade to unit 16 only to describe the interconnection and cooperationbetween the circuits.

Unit 15 is provided with inputs of detector input 21 and alternatingcurrent (AC+) power input 22. Detector input 22 also shown in FIG. 1, isconnected to terminal 23 of detector switch 24 of area detector 10.Connected to the remaining terminal, terminal 25 of switch 24 is analternating current source (AC+) which for the present purposes will bedenoted as the side of such source.

Detectors 10 and 12 are means which detect the presence of a vehicle ina defined area. In the instant case, induction loop detectors areutilized for detectors l0 and 12 which operate on a radiantelectromagnetic field principle, wherein a loop conductor 26 connectedto switch 24 is supplied with a given frequency of alternatingelectrical energy. As a vehicle enters the area defined by loopconductor 26, the electromagnetic field is altered by the Ferromagneticor magnetizable mass of the vehicle, thereby changing the frequency ofthe field and of the alternating electrical signal appearing onconductors 27 connected to switch 24. Switch 24, responds thereto andcloses a contact connected between terminals 23 and 25. Accordingly,terminals 23 and 25 in a rest or open condition are insulated From oneanother, in the absence of vehicles within loop conductor 26 while thesame terminals are in an activated or closed condition, shorted togetherwhen an automobile is present within the detector area.

Thus, detectors 10 and 12 provide a means for detecting the presence oftraffic within the approaches proximate the controlled intersection, andprovide information for operating the switching circuitry of the instantinvention. If desired, other types of detection means may be utilized,however, it has been found that the type of induction detectorsdescribed herein are very reliable and best suited for use in thepresent inventlon.

Considering now the operation of area detectors 10 and 12 with controlunits 15 and 16, as a car for example, car 11, enters induction loop 26,switch 24 shorts terminals 23 and 25 and applies AC(+) to detector input21 of control unit 15. Now as best shown in FIG. 2, AC current flowingbetween terminal 25 of detector switch 24, see FIG. 1, and terminal 29connected to AC(-), see FIG. 2, activates an M relay coil throughnormally closed contacts 30 and 31 of an R relay. The M relay and itsassociated contacts thus provide a detector controlled switching meansoperating between first and second modes in response to the presence orabsence of traffic in the associated approach. In its second or in thiscast activated mode AC(+) applied to input 22 passes through normallyopen contacts 32 and 33 (now closed) of the M relay, energizing a delaynetwork comprising diode 35, resistors 36, 37 and 38, and capacitor 39.After a preselected delay, which may typically vary between 10 and 20milliseconds, the green light of signal lights 19 is turned on by meansof a solid-state switching circuit 41, see FIGS. 1 and 3, in response toa signal appearing at terminal 40. The operation of this delay networkis provided by the rectification of the AC current by diode 35 and theeventual charging of capacitor 39 through resistor 36 providing aunidirectional voltage across resistors 37 and 38 a portion of which isapplied to terminal 40 via line 42. The purpose and advantage of thisdelay is to permit contacts 43 and 44 (previously opened) of a P relayto close securing firm electrical connection therebetween such that ACpower may be supplied to signal light switching circuits 41 throughterminal 81 and the above-mentioned contacts 43 and 44. It will be notedthat the P relay coil is in an energized state during the operation ofvehicle control unit 16. This is, the normally open contacts of the Prelay, for example, contacts 43 and 45 are closed during time periods inwhich unit 16 was in operation passing traffic appearing in the Bapproach through the intersection.

During the operation discussed above, as the M relay coil is energized,M relay normally closed contact 32 and 34 are open preventingenergization of the P relay coil and thereby disabling unit 16 asdiscussed more fully hereinafter.

Upon the activation of the M relay in response to vehicle detection,power is supplied to the coil of an N relay from power input 22, throughline 46, normally closed P relay contacts 43 and 44, line 47, normallyopened M relay contacts 48 and 49, and terminals 52 and 53 of primer 51,and through the end relay coil to AC(-). As the N relay is energized,normally open contacts 57 and 58 thereof close, latching the N relay inits energized state and normally closed contacts 61 and 62 thereof openinterrupting AC power applied to terminal 64 through contacts 61 and 62and resistor 63 and thereby extinguishing the red or stop light ofsignal lights 19 controlled by solid-state switching circuit 41.

As soon as car 11, shown in FIG. 1, passes over and leaves loopconductor 26 of detector 10, terminals 23 and 25 of detector switch 24open and consequently removes power from the coil of the M relay. Assoon as this occurs, and the M relay is deenergized, the normally opencontacts 32 and 33 thereof open and thereby terminate the proceed orgreen light of signal light 19. Additionally, normally closed contacts32 and 34 of the M relay close at this point applying AC power throughnormally open contacts 71 and 72 (now closed) of the N relay throughresistor 76 to terminal 75 actuating the caution or yellow lightindication of signal lights 19. It will be appreciated that the N relayis still in its energized state due to the latching thereof on its ownnormally open contacts 57 and 58, and thereby remains energized eventhough the M relay has deenergized.

At the same time that the caution indication is given at signal lights19, the coil of an R relay is energized through diode 78 and resistor 79which causes normally closed R relay contacts 30 and 31 to open therebypreventing actuation of the M relay by detector 10 during clearance ofthe intersection, that is during the caution light signal. The R relaycoil is operated by a rectified and filtered AC signal providedrespectively by diode 78 and shunt capacitor 80 and thus provides aprevent switching means disabling operation the M relay upon actuationthereof,

Concurrently with the caution indication, as the M relay is deenergized,normally closed contacts 49 and 50 thereof close supplying AC(+) powerfrom input 22 through terminal 54 of timer 51 through line 46, normallyclosed P relay contacts 43 and 44, line 47, normally open N relaycontacts 57 and 58, and M relay contacts 49 and 50. This connection,starts timer 51 which after a preselected interval deenergizes the Nrelay coil by shorting terminal 53 to terminal 55 as discussed herein.Terminal 55 of timer 51 is connected to AC().

As the N relay is deenergized, normally open contacts 71 and 72 thereofare opened removing the signal to terminal 75 and thereby extinguishingthe yellow or caution light of signal lights 19. In effect the N relayand timer 51 operate as a caution timer switching means for activatingthe caution condition of signal lights 19 for a preselected intervalafter the M relay resumes its first or nonactuated mode.

Additionally, normally closed contacts 61 and 62 of the N relay againclose and thereby actuate the red or stop light signal at signal lights19.

In summary of the forgoing, a system is provided for controlling trafficflow along approaches to a region of conflicting movement, includingdetector means for detecting the presence of traffic in each ofa numberof approaches, means for signalling stop and proceed conditions for eachof the several approaches, a switching means (M relays) for respondingto such detection of traffic and switching the signal means from anormal stop condition to a proceed condition for each approach in whichtraffic is detected and means for preventing the signals from displayinga proceed indication for one approach during a proceed indication forthe other approach. Particularly, vehicle control unit 15, responds toan approaching vehicle by means of detector and switches signal lights19 from a red to a green condition. As the vehicle passes into theintersection, thus leaving the boundaries of area detector 10, unitcauses signal lights 19 to cycle from a proceed indication through atimed interval of the caution indication and finally back to thenormally stop indication.

Similarly, vehicle control unit 16, operates in response to detection ofthe presence or approach of a vehicle in approach B by means of areadetector 12 and causes a green or proceed signal to appear at lights 18which eventually cycles through caution to a stop indication as thevehicle proceeds through the intersection.

As an important aspect of the present invention, control unit 15 and 16are connected together as shown in FIGS. 1 and 2 to provide forinstantaneous sharing of the intersection proper according to theimmediate traffic demands. ln other words, the particular cooperation ofcontrol units 15 and 16 permits allocation of nonconflictingintersection space in response to approaching or awaiting vehicles.Specifically, as illustrated in FIGS. 1 and 2, an output terminal 83 ofcontrol unit 15 is connected to an input terminal 22 of unit 16 while arelease terminal 93 of unit 15 is connected to a rest terminal 95 ofunit 16. As most clearly shown in FIG. 2, connection between terminals83 and 22 supplies AC power to unit 16 only when the P relay of controlunit A is energized and contacts 43 and 45 thereof are closed.Furthermore, connecting line 94joining unit 15 release terminal 93 withunit 16 rest terminal 95 provides power to energize the P relay coil ofunit 15 only when the M or N relays of unit 16 are in an energizedstate. In other words, the P relay coil of unit 15 will be cnergizedthrough input 22, normally closed contacts 32 and 34 of the M relay ofunit 15, normally closed contacts 71 and 73 of the N relay of unit 15,through the P relay coil of unit 15 to release terminal 93 thereof andthrough line 94 to unit 16 rest terminal 95 and through either the unit16 M or N relay contacts 68-65 or 8990 to AC().

The cooperation between units 15 and 16 will be described by .means ofseveral examples. First, consider the case where approach A is absent ofvehicles and approach B by means of detector 12 senses an oncoming car.Vehicle control unit 16 responds thereto causing the M relay thereof toclose, thus closing normally open M relay contacts 86 and 85. Thisconnection places rest terminal of unit 16 at AC() and thereby energizesP relay of unit 15. Normally open P relay contacts 43 and 45 of unit 15accordingly close connecting AC(+) power from input terminal 22 of unit15 to input terminal 22 of unit 16. Unit 16 is now in condition toswitch signal lights 18 from a red to a green state and accordingly doesso in the manner described in reference to unit 15 above. it will benoted that the P relay of unit 15 remains energized through releaseterminal 93 of unit 15 and rest terminal 95 of unit 16 throughout thegreen and yellow light condition of signal lights 18 and the P relay ofunit 15 opens only after unit 16 has cycled signal lights 18 back to thestop or red condition.

Now consider a second situation where a steady stream of 1 carstraveling over detector 10 in approach A is operating control unit 15providing a continuous green or proceed indication of signal lights 19.In this state, unit 15, M and N relays are energized connecting normallyopen M relay contacts 32 and 33 are accordingly applying AC(+) power toterminal of timer 67. Now at this point with a green light indication onsignal lights 19, a car enters loop conductor 28 of detector 12 andthereby closes the M relay of unit 16. The P relay coil of unit 15cannot close due to open M relay contacts 32 and 34 and accordinglypower cannot be supplied to unit 16 rendering this unit disabled foroperation so long as unit 15 remains in operation passing approach Atraffic. However, with AC(+) applied to terminal 66 of timer 67 and AC()applied to terminal 69 of timer 67 to the R relay coil and releaseterminal 73 and timer through the R relay coil and release terminal 73timer 67 is actuated. After a preselected interval, timer 67 connectsterminal 66 with terminal 69 thereof and thereby energizes the R relay.Normally closed R relay contacts 30 and 31 accordingly open deenergizingthe M relay, which in turn closes normally closed M relay contacts 32and 34 and starts timer 51 for cycling through the yellow lightinterval. Upon termination of the yellow light interval, the N relay isdeenergized closing normally closed N relay contacts 71 and 73,supplying power through the P relay coil which in response theretocloses normally open P relay contacts 43 and 45 delivering AC power toinput 22 of unit 16.

Additionally, upon closure of normally open P relay contacts 43 and 45 arectified alternating current signal is applied through diode 84 of unit15 to the R relay coil thereby maintaining the R relay in an energizedstate such that R relay contacts 30 and 31 are maintained openpreventing unit 15 from being actuated during operation of control unit16.

Since AC power is now supplied to unit 16, its operation may proceed asnormal, switching signal light 18 from a red to a green state andeventually back through yellow to red again. This immediately abovedescribed sequence allows vehicles waiting in the B approach tointerrupt a steady stream of traffic flowing in the A approach after agiven substantial time period, fixed by a timer 67 of unit 15.

Now consider the reverse of the above situation, wherein approach B isundergoing a steady stream of traffic with a green light indication onsignal light 18 and a car approaches the intersection from Direction A.At variance with the con nections for unit 15, unit 16 release terminal93 is connected directly to AC(). Accordingly, with B unit in a greenlight condition, timer 67 thereof starts immediately without waiting fora response from unit 15, and fixes the maximum time duration at whichunit 16 will remain in the green light state.

As an example of the versatility of the present system, unit- 15 may beeasily modified to operate as a preempter control unit. Particularly, byremoving the connection of the R relay coil of unit 15 to releaseterminal 93 of the same unit the M' relay of unit 16 will be conditionedto response to detector 10 even during continuous traffic in approach B.Upon such an occurrence the M relay of unit A will immediately returnthe P relay of unit A to its unactivated state, disabling unit 16. Suchan arrangement is desirable in the case of emergency traffic such asfire equipment, where detector 10 would be arranged to respond only tothe emergency vehicles for immediately returning a proceed conditiontherefor.

Also, it will be appreciated that from the foregoing describedoperation, that any number of control units such as and 16 may becascaded to provide allocation of available intersection space for amultiplicity of approach lanes. Additionally, while the embodiment ofthe invention described in FIGS. 1 and 2 provides for maximum timeintervals for which any one approach lane can receive a green lightcondition, it has been found in practical applications that substantialgaps between vehicles, even in heavy traffic, occur such that awaitingvehicles on a cross street approach may efficiently share the availableintersection space without inducing the operation oftimers 67 of units15 and 16. Also, in view of this fact, it has been possible to extendthe portion of loop conducters 26 and 28 distal theintersection, back asfar as I00 feet from the intersection to provide for early green lightindication and thus reducing traffic slow down to a minimum.

To enhance the multilane traffic control capabilities of the instantsystem, a pair of auxiliary terminals 183 and 184 are provided for eachunit 15 and 16, to be shorted by normally open contacts 185 and 186 ofthe P relays. Terminals 183 and 184 may then be connected as shown inFIG. 8, to control AC power supplied to another unit, in a mannersimilar to normally closed P relay contacts 43 and 44,

Up to this point, the actual switching of signal lights 18 and 19 hasnot been discussed. For this purpose a pair of solidstate switchingcircuits 41 and 42 shown in FIG. 1 are employed to respond to thecontrol signals provided by control units A and B and in accordancetherewith switch the light lamps of signals lights 18 and 19. Whilecircuits 41 and 42 are shown separately in this instance, it will beappreciated that they form a portion of each control units and may ifdesired be incorporated in the circuitry thereof. Particularly, FIG. 3shows the schematic diagram for solid-state switching circuits 41 and42, each of which include a set of three solid-state switching devices98, 99 and 100, known in the art as triacs, a set of input terminals 40,75, 64, 81 and 107, and a set of output lines 108, 109 and 110 connectedto the signal lights 18 and 19. Each set of the input terminals tocircuit 41 and 42 are connected to the output terminals of likereference numerals of units 15 and 16. Briefly, the operation of each ofswitching devices 98, 99 and 100 provide for example, connection of ACpower between input 102 and output 103 of device 98 in response to agating signal applied to gate terminal 104 of device 98. Accordingly, aspower is supplied to the input of devices 98 and 99 through terminal 81from vehicle control unit 15, each such device will allow power to flowinto green lamp 105 and yellow lamp 106 in response solely to thepresence of separate gating signals at terminals 40 and 75,respectively.

Somewhat at variance with the operation of devices 98 and 99, apermanently connected AC(+) supply is provided to terminal 107 and thusto the input of device 100, for energizing red lamp 111 solely inresponse to the presence of a gating signal at terminal 64. The purposeof supplying power to devices 98 and 99 through terminal 81 which iscontrolled by normally closed P relay contacts 43 and 44 of units 15 and16 is to prevent spurious and erroneous green or yellow lightindications for one approach during a green or yellow light indicationin the remaining direction thereby to a large degree eliminating thepossibility of conflicting traffic movement. On the other hand, red lamp111 is normally lit in the absence of approaching traffic in eitherdirection and, therefore, receives a permanent supply of powercontrolled only by a red gating signal appearing at terminal 64 of units15 and 16. Thus circuits 41 and 42 cooperate with the P relays of thecontrol units to provide supervisory circuit means to insure consistentoperation of the approach signal lights 18 and 19.

The combination of solid-state switching devices for controlling thepower supply to the lamp loads together with electromagnetic relays forperforming various logical functions, takes advantage of the most usefulcharacteristics of each class of device. Particularly, relay contactstend to disintegrate after periods of constant high current loadswitching, yet operate very efficiently for switching low current suchas found in the logic circuit. The solid-state switching devices,particularly triacs, on the other hand perform most advantageously underhigh current load switching conditions such as in the caseofincandescent lamp loads.

Timers 67 and timer 51 of unit 15 and 16 are shown in detail by FIGS. 4and 5. Timer 67 having terminal 66, 69 and 68 corresponding with likereference numerals in FIGS. 2, 6 and 7 provide for allowing a rectifiedalternating current signal to pass through resistors 124, 119 and 118charging capacitor 122 upon application of AC across terminals 66 and69. Diode 113 together with capacitor 114, the latter of which isconnected to AC() at terminal 68 provides rectification and filtering ofthe AC source such as to present a relatively unidirectional voltageatjunction 115 with respect to terminal 69. In the presence of suchvoltage capacitor 122 begins to charge through resistor 119 and variableresistor I18 and upon reaching a preselected voltage value switchesunijunction transistor 116 to a low impedance state. Upon reaching sucha low impedance state, the potential at control electrode of siliconcontrolled rectifier (SCR) 112 changes rapidly and thereby switches SCR112 to a low impedance mode. Zener diode 117 maintains a constantcharging voltage across capacitor 122 to insure uniformity of timing.Resistors 124, 123, 120 and 121 are biasing resistors which maintain SCR112 and unijunction transistor 116 in a quiescent condition suitable forswitching thereof. Accordingly, timer 67 provides for the passage ofgenerally unidirectional current between terminals 66 and 67 after apreselected time interval, which may be adjusted by variable resistor118, of AC power connected across terminal 66 and 69. Thus, timer 67provides a means for energizing the R relay coil shown in FIG. 2 so asto provide a maximum time interval during which a single approach maydominate the intersection.

Timer 51 illustrated in detail in FIG. 5, includes terminals 52, 53, 54and 55 corresponding to like reference terminal numbers in FIG. 2. Timer51 is particularly advantageous, in that it operates with a relativelyhigh power current sufficient for directly energizing and deenergizing arelay coil. That is, most timers are low power devices, which are notcapable of supplying sufficient current to operate a relay coil directlyand must use intermediate switching means connected between the timerand the relay coil for supplying operational current thereto. On theother hand, a timer 51 operating on an AC power source, is capable ofdirectly energizing and deenergizing the N relay coil as in FIG. 2thereby eliminating an additional switching component. Specifically,referring to FIG. 2 and 5, upon application of AC to terminal 52, timer51 operates to energize the N relay coil through terminal 53 and AC().This condition of the timer will continue until AC(+) is applied toterminal 54 which in combination with AC() connected to terminal 55initiates charging of capacitor 126. After a preselected intervaldetermined by the rate of charging capacitor 126, which may becontrolled by variable resistor 136, unijunction transistor 127 isswitched to a low impedance state, which in turn rapidly changes thevoltage applied to gate 129 of silicon controlled rectifier 128. Inresponse thereto, SCR 128 switches to a low impedance state therebyeffectively shorting terminals 53 and 55 together deenergizing the Nrelay coil. Diode 131 together with resistors 132 and 133 and capacitor140 provide for rectifying and filtering the AC signal applied acrossterminals 52 and 53 and as mentioned above, provide for passing currentenergizing the N relay coil. Diode 137 together with resistors 134 and135 and variable resistor 126 provide for introducing current forcharging capacitor 126 upon application of AC across terminals 54 and55. Zener diode 138 and capacitor 139 stabilize the charging current forcapacitor 126 thereby insuring uniformity of timing intervals. Resistorprovides for biasing transistor 127 and SCR 129.

Referring now to FIG. 6, a schematic diagram is shown ofa vehiclecontrol unit similar to that ofunits 1S and 16, shown in FIG. 2, butfurther including the features of advancing called detection and all redoverlap. The operation of this unit is the same as the basic controlunit, units and 16, with the exception that provision is made foradvance detection of vehicles approaching the intersection. The purposeof the advance calling detection feature is to permit an on-comingvehicle to obtain a green light signal at a greater distance from theintersection during light traffic for efficient flow thereof.Additionally, the control unit shown in FIG. 6 allows for greater gapsto occur between the approaching vehicles during the first part of thegreen interval without inducing a reversion of the signal light to itsred condition.

For this purpose, an additional or advance detector would be attached toadvance detector input 41, which in turn con nected to detector input 21through normally closed L relay contacts 142 and 143. In thisconfiguration, the M relay coil can be energized by a signal from eitherdetector. The advanced calling detector would be an area type detectorsimilar to those described in FIG. 1 arranged proximate the principaldetector upstreet from the intersection. As a car proceeds toward theintersection, the advance detector input 141 would first respond,energizing the M relay through the normally closed contacts of the L andR relays, respectively 142 and 143 and 30-31. With M relay energized,timer 67a starts timing a preselected interval due to the application ofAC(+) power to terminal 66a through normally open M relay contacts 32and 34 (now closed). Upon termination of the timing sequence, the Lrelay coil is energized via a connection'may be timer 67a betweenterminals 66a and 69a thereof. At this point normally closed L relaycontacts 142 and 143 open thereby leaving only the principal detectorconnected to detector input 21 to respond to vehicle movement orpresence. In effect, the L relay and timer 67a functions as an advancetiming means for conditioning the M relay to respond to the advancedetector only for a preselected time interval if the M relay isthereafter continuously maintained in its activated condition.Subsequent action of the vehicle control unit illustrated in FIG. 6 isthe same as described above, in reference to FIG. 2 except for theall-red overlap feature.

The all-red overlap provides for separating otherwise adjacent yellowlight and green light indications by a preselected red light timeinterval. For this feature, relay K and timer 510 are included in thecircuit of FIG. 6. Particularly when M relay energizes, normally opencontacts 48 and 49 close, energizing the N relay coil through timer 51.In response thereto, N normally open relay contacts 145 and 146energizes the K relay coil through timer 51a through terminals 52a and53a, thereupon the K relay locks on its own normally open contacts 147and 148. Therefore, relays M, N and K are all energized during the greenlight condition. As discussed in reference to FIG. 2, a yellow lightcondition is timed by timer 51. Additionally by means of closing ofnormally closed N relay contacts 149 and 146 and opening of the normallyopen N relay contacts 145 and 146 a timing sequence at timer 51a isinitiated. Also, normally closed N relay contacts 61 and 62 closecompleting the circuit to the red light gate, terminal 64. When timer51a times out, the K relay coil is deenergized and closes normallyclosed K relay contacts 150 and 151 completing normally closed K relaycontacts 150 and 151 completing the circuit to the P relay coil so as toallow other cascaded vehicle control units to respond to a vehicledemand. The K relay when energized additionally provides power, throughnormally open contacts 151 and 152 thereof, to the R relay coil viadiodes 92 and resistor 79 so as to maintain the R relay energized duringthe red light overlap period. Also, it is noted that K relay contactsI53 and 154 provide for connecting rest terminal 95 to AC() during thisperiod. The result of this arrangement is to disable other cascadedcontrol units for a certain time period determined by timer 51aimmediately after the control unit reverts to its red light condition.The advantage gained is to allow additional time for the intersection toclear before vehicles are permitted to proceed from the remainingapproaches.

The circuit of FIG. 6 may be connected in cascade with a like or similarunit in the manner as described in conjunction with FIGS. 1 and 2 forvehicle control units 15 and 16.

Up to this point in the description, no provision has been made forcontrolling pedestrian traffic. However, the method and apparatus of thepresent invention is readily adapted for such purpose. Specifically,FIG. 7 illustrates a schematic diagram of a pedestrian control unitespecially adapted for cooperating with vehicle control units such asthose shown in FIG. 2 and FIG. 6. Pursuant to the invention, theprinciple or basic operation of the pedestrian control unit is the sameas that of the vehicular control units. Exceptions are a provision forlimiting the maximum walk" interval (corresponding to green light orproceed interval) and a provision for delaying the walk indicationsindependently of reoccurring demands until a certain time interval haselapsed. This latter feature is particularly advantageous in cooperationwith the vehicular control unit for the following reason. If thevehicular movement is light in both directions of travel, the greenlight intervals presented in response thereto are very short, in therange of 2 seconds allowing efficient use of the intersection. However,minimum pedestrian walk" intervals are much longer, on the order of 15seconds. If pedestrians are permitted to move each time a vehicle isgiven a green indication, pedestrian traffic will accordingly determinethe timing of the intersection, greatly reducing the efficiency ofvehicular control. For this reason, the features of the presentinvention provide for collecting of pedestrians for selected timeintervals, typically in the range of 30 seconds. After such collection,the pedestrians are allowed to cross the street with the nextnonconflicting vehicular interval. In the meantime, several cycles ofvehicular intersection transversals, in both directions, may take place.

Referring now to FIG. 7, a pedestrian calling detector, pushbuttonswitch 160, is serially arranged between an AC(+) power source anddetector input 21 and substitutes for the function of vehicle detectorsl0 and 12 shown in FIG. 1. Output terminals 161 for a walk signal;terminal 162, for a flashing dont walk" signal; 163, for a constant dontwalk signal and 164 for AC power corresponding to output terminals 40,75, 64 and 81 in FIG. 2 provide for the control of the pedestrian signallights.

As in the case of the embodiment described in FIGS. 1, 2 and 3, it ispreferred that outputs at terminals 16l165 operate the correspondinglamp loads through a solid-state switching circuit so as to avoiddeterioration of the relay contacts with the control unit itself. Outputterminals 93, 83, and 95, are respectively the release output and restterminals of control unit A shown in FIG. 2. Similarly, AC(+) powerinput 22 of FIG. 6 corresponds to inputs 22 in FIG. 2.

In operation, as pushbutton switch is momentarily depressed in responseto a pedestrian call, a circuit is completed from AC(+) through switchI60, through normally closed G relay contacts and 176, through terminals52 and 53 of timer 51 completing the circuit through the E relay coiland locking the E relay on normally open E relay contacts 166 and 167.Timers 61b and 51c are ofthe same type of timer as illustrated in FIG.4. As the E relay closes, power supplied to the M relay coil throughnormally open E relay contacts 169 and 170, and normally close F relaycontacts 171 and 172. Particularly, the E relay and timer 51b functionas a pedestrian timer switching means for controlling the mode of the Mrelay in response to actuation of the pedestrian calling detector.

When AC power is applied to input 22 from another cascaded control unit,for example vehicular control units 15 or 16 of FIG. 2, a walkindication is given in response to AC power being applied to walk"terminal 161 through now closed M relay contacts 32 and 33. At the sametime, AC power will be delivered 54b of timer 51b commencing its timingoperation. Upon termination of this timing operation, relay E willdeenergize opening the circuit to the M relay by opening E relaycontacts 169 and 170. As the M relay drops out, the walk" lightindicating signal is extinguished and the flashing dont walk" signal isactuated at terminal 162 through previously closed N relay contacts 71and 72.

The remainder of the operating characteristics of this pedestriancontrol unit are the same as that of the above described vehicular unitA except for the provision of lock out timer, timer 51d. The purpose oftimer 51d is to prevent the immediate reoccurrence of a walk" lightindication after a previous pedestrian crossing. As mentioned above,this feature avoids pedestrian domination of the signal controlled intersection. In operation, relays N and M energize at the same time inthe normal manner. Relay N contacts 181 and 182 close energizing the Grelay coil through terminals 52d and 53d of timer 51d whereupon the Grelay locks upon its own normally open contacts 178 and 179.

Upon termination of the flashing "don't walk" interval (which correspondto the yellow or caution signal in the vehicle control units) the Nrelay deenergizes and the normally closed contacts 180 and 181 thereofclose the circuit to terminal 54d of timer 51d thus initiating itstiming cycle. On the terminal of this cycle, the G relay is deenergizedby the shorting of timer terminals 53d and 55d. The object of thisaction is to disable switch 160 from activating the E relay, after animmediately proceeding pedestrian crossing by means of the open G relaycontacts 175 and 176 until timer 51d marks offa preselected intervalthus the G relay together with timer 51c provide a prevent timerswitching means so as to avoid pedestrian dominance of the intersection.As discussed above, this timed interval which may be in the range of 30seconds, allows efflcient vehicular traffic movement while pedestriansare collected for eventual crossing.

it is noted that in the pedestrian control unit shown in FIG, 6, the Frelay provides a similar prevent function to that of the R relaydescribed in previous embodiments of the invention. Particularly,normally closed F relay contacts 171 and 172 open the circuit to the Mrelay coil in response to energization of the relay coil which occursupon demand by another control unit through release terminal 93. Atvariance with the circuits shown in FlGS. 3 and 6, however, theactuation of the F relay is not delayed through a timer but occurspromptly upon demand, opening contacts 171 and 172 so as to preventfurther pedestrian control of the M relay.

it will be apparent that each of the circuits shown in FIGS. 2, 6 and 7have a common basis of operation, this is evidenced by the reoccurrenceof the M relay which is responsive to the vehicle or pedestrian trafficand provides for displaying proceed indications in accordance therewith,and the reoccurrence of the P relay in each of the units, which provideswith switching circuits 41 and 42 for disabling the operation of one ofthe units during conflicting operation of the other and insuring againsterroneous conflicting signal indications. It is this common basis ofoperation which provides for the extreme versatility and flexibility ofthe invention. For example, as shown in FIG. 8 a three-phase vehicularand pedestrian control system is readily assembled through the use ofthree vehicle control'units 200, 201 and 203, each identical to controlunit 15 shown in FIG. 2 and a pedestrian control unit 205 identical tothe pedestrian control unit shown in H0. 7. in a manner similar to thatdescribed in conjunction with FIG. 1, control unit 200 provides forswitching signal lights 219 for A approaches, unit 201 provides forswitching signal lights 218 for B approaches, unit 202 switches signallights 220 for a lefthand turn approach C and pedestrian control unit205 operates signal lights 22] for controlling pedestrian traffic alongthe B direction. Only the output terminals of the control units areshown for convenience, each having a reference numeral corresponding tothe terminal numbers shown and described in detail hereinabove. Forexample, unit A has a detector input terminal 21 connected to detectorswitches 24 for the A approaches, control unit 201 has a detector input21 connected to detector switches 24 for the B vehicle approaches,control unit 202 similarly has a detector input 21 connected to detectorswitch 24 for the left-hand turn C approach while pedestrian controlunit 205 has a detector input 21 connected to pedestrian detectorswitches 160 for the B direction.

Each of control units 200-202 have signal control output terminals 40,75, 64 and 81 connected to solid-state switching devices 98, 99 and 100in the manner described for switching each of signal lights 219, 218 and222. Pedestrian control unit, 205, similarly has output terminals 161,162 163 and 164, a pair of solid-state switching devices 208 and 209 forswitching pedestrian signal lights between walk and don't walk"indications. It is noted in this regard, that terminal 162 of pedestriancontrol unit 205 which provides for the dont walk signal indication isnot used in this instance.

Now in regard to the connections of each of the units for providing thesequential operation thereof in accordance with instantaneous trafficdemands, vehicle control unit 200 has released terminal 93 thereofconnected to rest terminals 95 for each of control units 201, 202 and205 for preventing operation ofunit 200 during proceed and walkindications and caution indications for units 201, 202 and 205.Additionally, vehicle control unit 200 has power output terminal 83connected to AC power input terminals 22 of vehicle control unit 201 andpedestrian control unit 205 for preventing operation of these latter twounits during a proceed or caution operation of unit 200 for the Aapproaches.

Control unit 202, providing for left-hand turns from the C approachreceives power to input terminal 22 thereof, from output 83 of controlunit 200 through auxiliary terminals 183 and 184 of pedestrian controlunit 205, so as to disable control unit 202 for the C approach not onlywhen control unit 200 is operating to pass traffic from the A approachesbut also during passage of pedestrians in the C direction. That is,during operation of unit 200 passing vehicles in the A direction, poweris interrupted at output terminal 83 of unit 200 preventing power fromreaching input terminal 22 via unit 201 and 205. During operation ofunit 201, power is interrupted at output terminal 83 thereof againpreventing unit 202 from receiving power at input terminal 22 thereofthrough pedestrian unit 205. During operation of pedestrian control unit205, power is interrupted at auxiliary terminal 184 again preventingoperation of unit 202.

Additionally, in this example, each of release terminals 93 for units101, 102 and are connected to AC() so as to provide a maximum time outinterval during which each of control units 101, 102 and 105 maymaintain a proceed indication. At variance with this operation, unit 200having release terminal 93 connected to the rest terminals 95 of each ofunits 201, 202 and 205 providing such a maximum time out interval forunit 200 only in the event vehicle or pedestrian traffic is waiting inthe B approaches or if vehicle traffic is waiting in the left hand turnC approach. Accordingly, in the instant case, it is anticipated that theA approaches are oriented along the direction of the main streettraffic, so as to allow a continuous stream of traffic therealong tomaintain a continuous proceed indication until the traffic approachesthe intersection along one of the other directions.

It is noted that several of the terminals for each of the control unitsremain unconnected, for example rest terminal 95 of unit 200. Asindicated above, due to the universal characteristics of each of theunits, allowing for mass production and modular assembly, it is notalways necessary or desirable to utilize each and every function of theunits. However, by providing identical and universal units which may besold separately and assembled into a system according to therequirements of a particular intersection or traffic control problem,extreme versatility is obtained together with economy in manufacturingthe circuits.

As an example of this versatility, it will be appreciated thatconcurrent movements of trafflc may be provided if desired for certainintersections, such as concurrent left-hand turns from the C approachtogether with nonconflicting movement of trafiic from the right-handside A approach. Additionally, overlapping movements may be providedfor, wherein a first approach to an intersection is allowed to proceedconcurrently with adjacent but separate movements of traffic from two ormore approaches. That is, movement in the first direction overlaps themovement in the remaining several directions. Further still, preemptortraffic operations are readily adapted to the instant system asdiscussed above, allowing for emergency traffic situations atintersections for example near a fire station. ln this situation,separate detection of the emergency traffic by a separate control unit,would immediately interrupt operation of each of the remaining controlunits so as to allow preemption thereof.

We claim:

1. A system for controlling traffic through an intersection having atleast first and second approaches thereto, wherein the traffic in saidfirst approach is characterized by vehicles exhibiting a substantialmagnetizable mass, comprising in combination:

first detector means associated with the first approach characterized byan electromagnetic sensor productive of an electromagnetic field withina region of the first approach proximate the intersection and beingresponsive to such vehicles within said field to assume its actuatedcondition, and having a rest condition and an actuated condition andbeing responsive to the presence of traffic in the first approach toassume its actuated condition;

second detector means associated with the second approach characterizedby having a rest condition and an actuated condition and beingresponsive to the presence of traffic in the second approach to assumeits actuated condition;

first detector controlled switching means operatively connected to saidfirst detector means and having first and second modes, said firstswitching means being responsive to said first detector means in itsrest condition to assume its first mode and being responsive to saidfirst detector means in its actuated condition to assume its secondmode;

second detector controlled switching means operatively connected to saidsecond detector means and having first and second modes, said secondswitching means being responsive to said second detector means in itsrest condition to assume its first mode and being responsive to saidsecond detector means in its actuated condition to assume its secondmode;

supervisory circuit means operatively connected to said first and secondswitching means and having first and second states, said supervisorycircuit means being responsive to said first switching means in itssecond mode to assume its first state and being responsive to saidsecond switching means in its second mode and said first switching meansin its first mode to assume its second state;

first traffic signal means characterized by having mutually exclusivestop and proceed traffic directory conditions and positioned to indicateits condition to traffic in the first approach, said first signal meansoperatively connected to said supervisory circuit means together withsaid first switching means and being responsive to said supervisoryswitching means in its first state and said first switching means in itssecond mode to assume its proceed condition and responsive to saidsupervisory circuit means in its second state to assume its stopcondition;

second traffic signal means characterized by having mutually exclusivestop and proceed traffic directory conditions and positioned to indicateits condition to traffic in the second approach, said second signalmeans operatively connected to said supervisory circuit means togetherwith said second switching means and being responsive to saidsupervisory circuit means in its second state and said second switchingmeans in its second mode to assume its proceed condition and responsiveto said supervisory circuit means in its first state to assume its stopcondition;

first prevent switching means operatively connected to said first andsecond switching means and said supervisory circuit means and having anormal mode and a disabling mode, said first switching means responsiveto said prevent switching means in its disabling mode to assume andremain in its first mode, said prevent switching means being responsiveto said supervisory circuit means in its second state and said secondswitching means in its second mode to assume its disabling mode;

first time out switching means operatively connected to said first andprevent switching means, said time out switching means responsive tosaid first switching means in its second mode to actuate said preventswitching means to its disabling mode after a preselected time intervalwith said supervisory circuit means in its first state and said secondswitching means in its second mode;

second prevent switching means and second time out switching meansoperatively connected to said second switching means and saidsupervisory circuit means, said second prevent switching means having anormal mode and a disabling mode, said second switching means responsiveto said second prevent switching means in its disabling mode to assumeand remain in its first mode, said second prevent switching meansresponsive to said second time out switching means to assume itsdisabling mode after a preselected time interval with said supervisorycircuit means in its second state and said second switching means in itssecond mode;

advance detector means having a rest condition and an actuated conditionand being characterized by an electromagnetic sensor productive of anelectromagnetic field and responsive to the presence of such vehicleswithin said field to assume its actuated condition, said advancedetector means positioned to arrange its field within said approachadjacent the field of said first detector on the side thereof oppositethe intersection to respond to such vehicles approaching theintersection prior to the response of said first detector means; andadvance timer switching means operatively connected to aforesaid firstswitching means and said advance detector means and having a normalstate and a disabling state, said first switching means being responsiveto said advance detector means in its actuated condition and saidadvance timer switching means in its normal state to assume its secondmode, said advance timer switching means being responsive to said firstswitching means in its first mode to assume its normal state andresponsive to said first switching means being in its second mode for apreselected time interval to assume its disabling state. 2. A system forcontrolling traffic through an intersection having at least first andsecond approaches thereto, wherein the traffic in the second approach iscomposed of pedestrians, comprising in combination:

first detector means associated with the first approach characterized byhaving a rest condition and an actuated condition and being responsiveto the presence of traffic in the first approach to assume its actuatedcondition;

second detector means associated with the second approach characterizedby a manually operated switch disposed for operation by the pedestriansand responsive to such operation to momentarily assume its activatedcondition and having a rest condition and an actuated condition andbeing responsive to the presence of traffic in the second approach toassume its actuated condition;

first detector controlled switching means operatively connected to saidfirst detector means hand having first and second modes, said firstswitching means being responsive to said first detector means in itsrest condition to assume its first mode and being responsive to saidfirst detector means in its actuated condition to assume its secondmode;

second detector controlled switching means operatively connected to saidsecond detector means and having first and second modes, said secondswitching means being responsive to said second detector means in itsrest condition to assume its first mode and being responsive to saidsecond detector means in its actuated condition to assume its secondmode; supervisory circuit means operatively connected to said first andsecond switching means and having first and second states, saidsupervisory circuit means being responsive to said first switching meansin its second mode to assume its first state and being responsive tosaid second switching means in its second mode and said first switchingmeans in its first mode to assume its second state; first traffic signalmeans characterized by having mutually exclusive stop and proceedtraffic directory conditions and positioned to indicate its condition totraffic in the first approach, said first signal means operativelyconnected to said supervisory circuit means together with said firstswitching means and being responsive to said supervisory switching meansin its first state and said first switching means in its second mode toassume its proceed condition and responsive to said supervisory circuitmeans in its second state to assume its stop condition;

second traffic signal means characterized by having mutually exclusivestop and proceed traffic directory conditions and positioned to indicateits condition to traffic in the second approach, said second signalmeans operatively connected to said supervisory circuit means togetherwith said second switching means and being responsive to saidsupervisory circuit means in its second state and said second switchingmeans in its second mode to assume its proceed condition and responsiveto said supervisory circuit means in its first state to assume its stopcondition;

first prevent switching means operatively connected to said first andsecond switching means and said supervisory circuit means and having anormal mode and a disabling mode, said first switching means responsiveto said prevent switching means in its disabling mode to assume andremain in its first mode, said prevent switching means being responsiveto said supervisory circuit means in its second state and said secondswitching means in its second mode to assume its disabling mode;

first time out switching means operatively connected to said first andprevent switching means, said time out switching means responsive tosaid first switching means in its second mode to actuate said preventswitching means to its disabling mode after a preselected time intervalwith said supervisory circuit means in its first state and said secondswitching means in its second mode; and

a pedestrian timer switching means operatively connected between saidsecond detector means and second switching means and having a normalstate and an actuated state, said pedestrian timer switching meansoperative in its normal state to maintain said second switching means inits first mode and operative in its timing state to activate said secondswitching means to its second mode for a preselected time interval, saidpedestrian timer switching means responsive to said second detectormeans being momentarily in its activated condition to assume its timingstate until termination of said interval.

3. A system as defined in claim 2, further comprising prevent timerswitching means operatively connected between said second detector meansand said pedestrian timer switching means and having a normal mode and adisabling mode, said prevent timer switching means operative in saidnormal mode to permit said pedestrian timer switching means to assumeits normal and timing states in aforesaid response to said seconddetector means and operative in its disabling mode to render saidpedestrian timer switching means nonresponsive to said second detectormeans.

4. A control unit for use in a traffic control system having a trafficdetector associated with one approach to an intersection and productiveofan electrical signal in response to tral'fic therein and anelectrically operated traffic signal having separate proceed, cautionand stop conditions also associated with such approach and electricalcontrol means for regulating traffic associated with another approach tothe intersection productive of an electrical signal indicating itsinstant mode of operation and reception of a source of operating power,wherein the control unit comprises;

a detector input adapted to be connected to the detector for receivingthe electrical signal therefrom,

a first electrical power input adapted to receive a controlled source ofelectrical power;

a second electrical power input adapted to receive a continuous sourceof electrical power;

a release input adapted to be connected to the control means forreceiving the electrical signal indicative of the instant operationalmode thereof;

an electrical power output adapted to be connected to the control meansunit for providing the controlled source of power therefor;

traffic signal proceed, caution and stop outputs adapted to be connectedto the traffic signals for providing electrical signals separatelyactuating its proceed, caution and stop conditions;

detector controlled switching means having first and second modes andbeing connected to said detector input, and said first power input, saiddetector controlled switching means being responsive to said detectorinput to assume its first or second modes in response to the electricalsignal appearing thereat;

supervisory circuit means having first and second states and beingconnected to said detector controlled switching means, said firstelectrical power input, said release input, said electrical power outputand said traffic signal proceed and caution outputs, said supervisorycircuit means being responsive to said detector controlled switchingmeans in its second mode to assume its first state and being responsiveto said detector controlled switching means in its first mode and thecontrolled source of power appearing at said first power input and theelectrical signal appearing at said release input to assume its secondstate, said electrical power output being responsive to said supervisorycircuit means in its second mode and the controlled source of powerappearing at said first power input to provide the controlled source ofpower for the control means, said traffic signal proceed output beingresponsive to said supervisory circuit means in its first state and saiddetector controlled switching means in its second mode, and thecontrolled source of power appearing at the said first power input toprovide the electrical signal for actuating the traffic signal to itsproceed condition; and

caution timer switching means having a normal and an actuated state andbeing connected to said supervisory circuit means, said detectorcontrolled switching means, said second power input, said traffic signalcaution output and stop output, said caution timer switching means beingresponsive to said supervisory circuit means in its first state and saiddetector controlled switching means in its second mode and thecontrolled source of power appearing at said first power input to assumeits actuated state being responsive to said detector controlledswitching means resuming its first mode to assume its normal state aftera preselected interval, said traffic signal caution output beingresponsive to said caution timer switching means in its normal state toprovide the electrical signal for actuating the traffic signal to itsstop condition.

5. in a system as defined in claim 4, wherein the control means isreceptive to an electrical signal indicating the instant operationalmode of the control unit and the control unit further comprises;

a rest output adapted to be connected to the control means,

said rest output being connected to said detector controlled switchingmeans and said caution timer switching means and being responsive tosaid detector controlled switching means in its second mode or saidcaution timer switching means in its actuated state to provide theelectrical signal at said rest output indicating the mode of the controlunit.

6. In a system as defined in claim 4, the control unit furthercomprising;

a prevent switching means connected to said detector controlledswitching means, said supervisory circuit means and said release inputand having a normal mode and a disabling mode, said detector controlledswitching means being responsive to said prevent switching means in itsdisabling mode to assume and remain in its first mode, said preventswitching means responsive to said supervisory circuit means in itssecond state and the electrical signal appearing at said release inputto assume its actuated mode.

7. in a system as defined in claim 4, the control unit furthercomprising;

time out switching means connected to said detector controlled switchingmeans and said prevent switching means, said prevent switching meansbeing responsive to said time out switching means and said detectorcontrolled switching means in its second mode and said supervisorycircuit means in its first state and the presence of the electricalsignal at said release input for a preselected time interval to assumeits disabling mode.

8. In a system as defined in claim 4, wherein said supervisory circuitmeans is responsive to said caution time switching means being in itsactuated state to remain in its first state.

9. In a system as defined in claim 6, the control unit as defined,wherein said prevent switching means is responsive to said caution timerswitching means in its actuated state and said detector controlledswitching means in its first mode to assume its disabling mode.

10. in a system as defined in claim 4, further characterized by anadditional traffic detector associated with the first named approach andproductive of an electrical signal indicative of traffic conditionstherein in advance of the first named detector, and the control unitfurther comprising;

an advance detector input adapted to be connected to the additiondetector for receiving the electrical signal therefrom; and

advance timer switching means having a normal state and a disablingstate and being connected to said advance detector input and saiddetector controlled switching means, said detector controlled switchingmeans being responsive to the electrical signal appearing at saidadvance detector input when said advance timer switching means is in itsnormal state to assume its first and second modes, said advance timerswitching means being responsive to said detector controlled switchingmeans being in its second mode for a preselected time interval to assumeits disabling state and being responsive to said detector controlledswitching means in its first mode to assume its normal state.

11. In a system as defined in claim 5, further characterized by thetraffic in the first named approach being composed of pedestrians andthe detector being a manually operated switch providing the electricalsignal therefor,

pedestrian timer switching means connected to said detector input andsaid detector controlled switching means and having a normal state andan actuated state, said detector controlled switching means beingresponsive to said pedestrian timer switching means in its actuatedstate to assume its second mode for a preselected time interval, saidpedestrian timer switching means being responsive to the electricalsignal appearing at said detector input and the source of power at saidsecond power input to assume and remain in its actuated state and beingresponsive to said supervisory circuit means being in its first stateand said detector controlled switching means being in its second modefor said interval to assume its normal state.

12. In a system as defined in claim 11, the control unit furthercomprising;

prevent timer switching means connected between said detector input andsaid pedestrian timer switching means and having a normal mode and adisabling mode, said pedestrian timer switching means being responsiveto said detector input, said prevent timer switching means further beingconnected to said second power input and said caution timer switchingmeans and being responsive to said second power input and said cautiontimer switching means in its actuated state to assume its disabling modefor a preselected interval.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,582,876 Dated June 1 1971 Inventor) Howard Carmack et a1 It is certifiedthat error appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Column 2, line 2, "non conflicting" should read Column 3 line 66 "From"should read from Column 6 line 26, "155" should read 66 lines 35 and 36,cancel "to the R relay coil and release terminal 73 and timer". Column10, line 72, after "delivered" insert to terminal Column 16, line 62,after "switching means" insert in its actuated state and said detectorcontrolled switching means in its first mode to provide the electricalsignal for actuating the traffic signal to its caution condition, saidtraffic signal stop output being responsive to said caution timerswitching means Signed and sealed this 18th day of January 1972.

(SEAL) Attest EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting OfficerActing Commissioner of Patents non-conflicting line 30, "d4awings"should read drawings FORM F'O-1 (10-69) USCOMM-DC 603764 69 9 U S.GOVERNMENT PRINTING OFFICE I969 D365'334

1. A system for controlling traffic through an intersection having atleast first and second approaches thereto, wherein the traffic in saidfirst approach is characterized by vehicles exhibiting a substantialmagnetizable mass, comprising in combination: first detector meansassociated with the first approach characterized by an electromagneticsensor productive of an electromagnetic field within a region of thefirst approach proximate the intersection and being responsive to suchvehicles within said field to assume its actuated condition, and havinga rest condition and an actuated condition and being responsive to thepresence of traffic in the first approach to assume its actuatedcondition; second detector means associated with the second approachcharacterized by having a rest condition and an actuated Condition andbeing responsive to the presence of traffic in the second approach toassume its actuated condition; first detector controlled switching meansoperatively connected to said first detector means and having first andsecond modes, said first switching means being responsive to said firstdetector means in its rest condition to assume its first mode and beingresponsive to said first detector means in its actuated condition toassume its second mode; second detector controlled switching meansoperatively connected to said second detector means and having first andsecond modes, said second switching means being responsive to saidsecond detector means in its rest condition to assume its first mode andbeing responsive to said second detector means in its actuated conditionto assume its second mode; supervisory circuit means operativelyconnected to said first and second switching means and having first andsecond states, said supervisory circuit means being responsive to saidfirst switching means in its second mode to assume its first state andbeing responsive to said second switching means in its second mode andsaid first switching means in its first mode to assume its second state;first traffic signal means characterized by having mutually exclusivestop and proceed traffic directory conditions and positioned to indicateits condition to traffic in the first approach, said first signal meansoperatively connected to said supervisory circuit means together withsaid first switching means and being responsive to said supervisoryswitching means in its first state and said first switching means in itssecond mode to assume its proceed condition and responsive to saidsupervisory circuit means in its second state to assume its stopcondition; second traffic signal means characterized by having mutuallyexclusive stop and proceed traffic directory conditions and positionedto indicate its condition to traffic in the second approach, said secondsignal means operatively connected to said supervisory circuit meanstogether with said second switching means and being responsive to saidsupervisory circuit means in its second state and said second switchingmeans in its second mode to assume its proceed condition and responsiveto said supervisory circuit means in its first state to assume its stopcondition; first prevent switching means operatively connected to saidfirst and second switching means and said supervisory circuit means andhaving a normal mode and a disabling mode, said first switching meansresponsive to said prevent switching means in its disabling mode toassume and remain in its first mode, said prevent switching means beingresponsive to said supervisory circuit means in its second state andsaid second switching means in its second mode to assume its disablingmode; first time out switching means operatively connected to said firstand prevent switching means, said time out switching means responsive tosaid first switching means in its second mode to actuate said preventswitching means to its disabling mode after a preselected time intervalwith said supervisory circuit means in its first state and said secondswitching means in its second mode; second prevent switching means andsecond time out switching means operatively connected to said secondswitching means and said supervisory circuit means, said second preventswitching means having a normal mode and a disabling mode, said secondswitching means responsive to said second prevent switching means in itsdisabling mode to assume and remain in its first mode, said secondprevent switching means responsive to said second time out switchingmeans to assume its disabling mode after a preselected time intervalwith said supervisory circuit means in its second state and said secondswitching means in its second mode; advance detector means having a restcondition and an actuated condition and being characterized by anelectromagnetic sensor productivE of an electromagnetic field andresponsive to the presence of such vehicles within said field to assumeits actuated condition, said advance detector means positioned toarrange its field within said approach adjacent the field of said firstdetector on the side thereof opposite the intersection to respond tosuch vehicles approaching the intersection prior to the response of saidfirst detector means; and advance timer switching means operativelyconnected to aforesaid first switching means and said advance detectormeans and having a normal state and a disabling state, said firstswitching means being responsive to said advance detector means in itsactuated condition and said advance timer switching means in its normalstate to assume its second mode, said advance timer switching meansbeing responsive to said first switching means in its first mode toassume its normal state and responsive to said first switching meansbeing in its second mode for a preselected time interval to assume itsdisabling state.
 2. A system for controlling traffic through anintersection having at least first and second approaches thereto,wherein the traffic in the second approach is composed of pedestrians,comprising in combination: first detector means associated with thefirst approach characterized by having a rest condition and an actuatedcondition and being responsive to the presence of traffic in the firstapproach to assume its actuated condition; second detector meansassociated with the second approach characterized by a manually operatedswitch disposed for operation by the pedestrians and responsive to suchoperation to momentarily assume its activated condition and having arest condition and an actuated condition and being responsive to thepresence of traffic in the second approach to assume its actuatedcondition; first detector controlled switching means operativelyconnected to said first detector means hand having first and secondmodes, said first switching means being responsive to said firstdetector means in its rest condition to assume its first mode and beingresponsive to said first detector means in its actuated condition toassume its second mode; second detector controlled switching meansoperatively connected to said second detector means and having first andsecond modes, said second switching means being responsive to saidsecond detector means in its rest condition to assume its first mode andbeing responsive to said second detector means in its actuated conditionto assume its second mode; supervisory circuit means operativelyconnected to said first and second switching means and having first andsecond states, said supervisory circuit means being responsive to saidfirst switching means in its second mode to assume its first state andbeing responsive to said second switching means in its second mode andsaid first switching means in its first mode to assume its second state;first traffic signal means characterized by having mutually exclusivestop and proceed traffic directory conditions and positioned to indicateits condition to traffic in the first approach, said first signal meansoperatively connected to said supervisory circuit means together withsaid first switching means and being responsive to said supervisoryswitching means in its first state and said first switching means in itssecond mode to assume its proceed condition and responsive to saidsupervisory circuit means in its second state to assume its stopcondition; second traffic signal means characterized by having mutuallyexclusive stop and proceed traffic directory conditions and positionedto indicate its condition to traffic in the second approach, said secondsignal means operatively connected to said supervisory circuit meanstogether with said second switching means and being responsive to saidsupervisory circuit means in its second state and said second switchingmeans in its second mode to assume its proceed condition and responsiveto sAid supervisory circuit means in its first state to assume its stopcondition; first prevent switching means operatively connected to saidfirst and second switching means and said supervisory circuit means andhaving a normal mode and a disabling mode, said first switching meansresponsive to said prevent switching means in its disabling mode toassume and remain in its first mode, said prevent switching means beingresponsive to said supervisory circuit means in its second state andsaid second switching means in its second mode to assume its disablingmode; first time out switching means operatively connected to said firstand prevent switching means, said time out switching means responsive tosaid first switching means in its second mode to actuate said preventswitching means to its disabling mode after a preselected time intervalwith said supervisory circuit means in its first state and said secondswitching means in its second mode; and a pedestrian timer switchingmeans operatively connected between said second detector means andsecond switching means and having a normal state and an actuated state,said pedestrian timer switching means operative in its normal state tomaintain said second switching means in its first mode and operative inits timing state to activate said second switching means to its secondmode for a preselected time interval, said pedestrian timer switchingmeans responsive to said second detector means being momentarily in itsactivated condition to assume its timing state until termination of saidinterval.
 3. A system as defined in claim 2, further comprising preventtimer switching means operatively connected between said second detectormeans and said pedestrian timer switching means and having a normal modeand a disabling mode, said prevent timer switching means operative insaid normal mode to permit said pedestrian timer switching means toassume its normal and timing states in aforesaid response to said seconddetector means and operative in its disabling mode to render saidpedestrian timer switching means nonresponsive to said second detectormeans.
 4. A control unit for use in a traffic control system having atraffic detector associated with one approach to an intersection andproductive of an electrical signal in response to traffic therein and anelectrically operated traffic signal having separate proceed, cautionand stop conditions also associated with such approach and electricalcontrol means for regulating traffic associated with another approach tothe intersection productive of an electrical signal indicating itsinstant mode of operation and reception of a source of operating power,wherein the control unit comprises; a detector input adapted to beconnected to the detector for receiving the electrical signal therefrom,a first electrical power input adapted to receive a controlled source ofelectrical power; a second electrical power input adapted to receive acontinuous source of electrical power; a release input adapted to beconnected to the control means for receiving the electrical signalindicative of the instant operational mode thereof; an electrical poweroutput adapted to be connected to the control means unit for providingthe controlled source of power therefor; traffic signal proceed, cautionand stop outputs adapted to be connected to the traffic signals forproviding electrical signals separately actuating its proceed, cautionand stop conditions; detector controlled switching means having firstand second modes and being connected to said detector input, and saidfirst power input, said detector controlled switching means beingresponsive to said detector input to assume its first or second modes inresponse to the electrical signal appearing thereat; supervisory circuitmeans having first and second states and being connected to saiddetector controlled switching means, said first electrical power input,said release input, said eleCtrical power output and said traffic signalproceed and caution outputs, said supervisory circuit means beingresponsive to said detector controlled switching means in its secondmode to assume its first state and being responsive to said detectorcontrolled switching means in its first mode and the controlled sourceof power appearing at said first power input and the electrical signalappearing at said release input to assume its second state, saidelectrical power output being responsive to said supervisory circuitmeans in its second mode and the controlled source of power appearing atsaid first power input to provide the controlled source of power for thecontrol means, said traffic signal proceed output being responsive tosaid supervisory circuit means in its first state and said detectorcontrolled switching means in its second mode, and the controlled sourceof power appearing at the said first power input to provide theelectrical signal for actuating the traffic signal to its proceedcondition; and caution timer switching means having a normal and anactuated state and being connected to said supervisory circuit means,said detector controlled switching means, said second power input, saidtraffic signal caution output and stop output, said caution timerswitching means being responsive to said supervisory circuit means inits first state and said detector controlled switching means in itssecond mode and the controlled source of power appearing at said firstpower input to assume its actuated state being responsive to saiddetector controlled switching means resuming its first mode to assumeits normal state after a preselected interval, said traffic signalcaution output being responsive to said caution timer switching means inits normal state to provide the electrical signal for actuating thetraffic signal to its stop condition.
 5. In a system as defined in claim4, wherein the control means is receptive to an electrical signalindicating the instant operational mode of the control unit and thecontrol unit further comprises; a rest output adapted to be connected tothe control means, said rest output being connected to said detectorcontrolled switching means and said caution timer switching means andbeing responsive to said detector controlled switching means in itssecond mode or said caution timer switching means in its actuated stateto provide the electrical signal at said rest output indicating the modeof the control unit.
 6. In a system as defined in claim 4, the controlunit further comprising; a prevent switching means connected to saiddetector controlled switching means, said supervisory circuit means andsaid release input and having a normal mode and a disabling mode, saiddetector controlled switching means being responsive to said preventswitching means in its disabling mode to assume and remain in its firstmode, said prevent switching means responsive to said supervisorycircuit means in its second state and the electrical signal appearing atsaid release input to assume its actuated mode.
 7. In a system asdefined in claim 4, the control unit further comprising; time outswitching means connected to said detector controlled switching meansand said prevent switching means, said prevent switching means beingresponsive to said time out switching means and said detector controlledswitching means in its second mode and said supervisory circuit means inits first state and the presence of the electrical signal at saidrelease input for a preselected time interval to assume its disablingmode.
 8. In a system as defined in claim 4, wherein said supervisorycircuit means is responsive to said caution time switching means beingin its actuated state to remain in its first state.
 9. In a system asdefined in claim 6, the control unit as defined, wherein said preventswitching means is responsive to said caution timer switching means inits actuated state and said detector controlled switching means in Itsfirst mode to assume its disabling mode.
 10. In a system as defined inclaim 4, further characterized by an additional traffic detectorassociated with the first named approach and productive of an electricalsignal indicative of traffic conditions therein in advance of the firstnamed detector, and the control unit further comprising; an advancedetector input adapted to be connected to the addition detector forreceiving the electrical signal therefrom; and advance timer switchingmeans having a normal state and a disabling state and being connected tosaid advance detector input and said detector controlled switchingmeans, said detector controlled switching means being responsive to theelectrical signal appearing at said advance detector input when saidadvance timer switching means is in its normal state to assume its firstand second modes, said advance timer switching means being responsive tosaid detector controlled switching means being in its second mode for apreselected time interval to assume its disabling state and beingresponsive to said detector controlled switching means in its first modeto assume its normal state.
 11. In a system as defined in claim 5,further characterized by the traffic in the first named approach beingcomposed of pedestrians and the detector being a manually operatedswitch providing the electrical signal therefor, pedestrian timerswitching means connected to said detector input and said detectorcontrolled switching means and having a normal state and an actuatedstate, said detector controlled switching means being responsive to saidpedestrian timer switching means in its actuated state to assume itssecond mode for a preselected time interval, said pedestrian timerswitching means being responsive to the electrical signal appearing atsaid detector input and the source of power at said second power inputto assume and remain in its actuated state and being responsive to saidsupervisory circuit means being in its first state and said detectorcontrolled switching means being in its second mode for said interval toassume its normal state.
 12. In a system as defined in claim 11, thecontrol unit further comprising; prevent timer switching means connectedbetween said detector input and said pedestrian timer switching meansand having a normal mode and a disabling mode, said pedestrian timerswitching means being responsive to said detector input, said preventtimer switching means further being connected to said second power inputand said caution timer switching means and being responsive to saidsecond power input and said caution timer switching means in itsactuated state to assume its disabling mode for a preselected interval.